1. Field of the Invention
The present invention relates to a secure FM-SCA broadcasting system having a central transmitting station for transmitting encoded data and subscriber actuated portable receiving terminals for decoding and displaying the data.
2. Description of the Prior Art
One of the problems associated with the buying and selling of securities and commodities has been satisfying the need for current information at locations remote from the various exhanges and other trading places. An initial solution by the stock brokerage houses was the direct display of information provided via teletype by the various exhanges. However, such a display either required a customer to visit his brokerage house or to phone his stockbroker and request that one or more stocks be watched. Since the information was transmitted and received in serial form, either method of obtaining the information required the expenditure of much time on the part of the person observing the display.
A subsequent solution was the development of a quotation terminal and high speed transmission of the data from a central data processing and storage unit. The terminal user, typically the stockbroker, could request information on a particular stock for immediate display. Still, there was the necessity to either call the stockbroker for current information or visit the brokerage house where the customer had access to the terminal. However, since most customers were reluctant to call the stockbroker where they were not contemplating a transaction and did not have the time available for frequent trips to the brokerage house, they did without the information. Such inaction tended to stifle transactions.
The difficulty in obtaining information and the high cost of a quotation terminal for an individual customer led to the development of a less expensive personal data terminal. One form of such a terminal is shown in U.S. Pat. No. 3,716,835 issued on Feb. 13, 1973. A data processor receives stock market information via teletype lines or other high speed lines and stores the data in a memory. A personal quotation terminal is connected to the data processor by telephone lines for bidirectional communication. The terminal includes an acoustic coupler for a telephone handset, a keyboard for entering address and control signals, and display means. The customer dials the telephone number of the data processor and when connected places the handset in contact with the acoustic coupler. The customer then enters the address of the desired stock information which is sent to the data processor over the telephone line. The data processor sends the current information through the telephone line to the terminal where it is displayed. However, such a system has the disadvantages of requiring that a telephone be available and that the data processor not be busy with inquiries from other customers. Potentially, a few customers could tie up all the telephone input lines by leaving their terminals connected to the data processor although they were not requesting information.
An alternate form of a personal quotation terminal which solves many of the problems associated with the telephone coupled system is shown in U.S. Pat. No. 3,611,294. The stock data is processed, encoded and transmitted by a modulated carrier wave. A plurality of portable receivers each separate the data from the carrier wave and compare a portion of the data representing a stock identification code with the code entered by the customer. If the codes are the same, the data is displayed. The terminal may be utilized on a subscription basis where a subscriber is provided with a punched card to be inserted into a translator. A stock code is set on a plurality of code wheels which cooperate with the translator to establish an identification code for the stock. However, since the terminal cannot be operated without the card, it is vunerable inoperation due to misplaced, lost or forgotten cards. Furthermore, a borrowed or stolen card permits unauthorized use and it is relatively easy to discover the card code for a new pay period by observing the transmitted data in the old and new pay periods and knowing card code for the old pay period.